Abstract A novel human coronavirus, hCoV-EMC, was recently identified in the Middle East. It was reported to cause severe acute respiratory syndrome (SARS)-like disease, having killed 5 persons and sickened 4 others since June of 2012. Because hCoV-EMC is genetically related to SARS-CoV, the causative agent of the deadly SARS that killed 774 people among 8,098 infected cases during the 2003 outbreak, it has raised great concerns about the potential pandemic spread of this lethal disease. Therefore, developing vaccines to prevent the potential outbreak of hCoV-EMC infection is urgently needed. We have previously shown that the receptor-binding domain (RBD) of SARS-CoV spike (S) protein S1 subunit contains critical neutralizing domain (CND) and that the subunit vaccine based on the RBD/CND can induce potent neutralizing antibody responses and protection against SARS-CoV infection in animal models. By comparing and analyzing the S protein sequences of SARS-CoV and hCoV- EMC, we found that hCoV-EMC S protein S1 subunit also contains a region that exhibited a core structure very similar to that of RBD in SARS-CoV S protein. We also found that a recombinant protein containing the truncated ectodomain of hCoV-EMC S protein fused to Fc induced S-specific antibodies with neutralizing activity, suggesting that hCoV-EMC S protein does contain CND(s). We therefore hypothesize that CND(s) can be identified from the hCoV-EMC S protein, based which an effective vaccine with ability to elicit strong neutralizing antibody responses and protective immunity against hCoV-EMC infection can be developed. The specific aims of this proposal are to: 1) identify CND(s) from hCoV- EMC S protein and its subunits, 2) design CND-based subunit hCoV-EMC vaccines, 3) optimize immunization regimens for vaccination of animals with a selected hCoV-EMC vaccine candidate, and 4) evaluate the in vivo protective immunity of the selected hCoV-EMC vaccine candidate against viral challenge in an animal model. The long-term goal of the proposed study is to develop an effective and safe CND-based subunit vaccine against the newly identified SARS-like virus hCoV-EMC that may cause a future outbreak in humans.